The invention relates to a device for detecting by the utilization of reflected light surface unevenness of a wire-shaped body which has a conductor covered with a light transmissive insulating material such as enamel. Such surface unevenness results primarily from raised portions such as may occur by the presence of particles.
In a typical device of this general type, light is shown upon such a wire-shaped body (hereinafter referred to merely as "a wire" when applicable) from obliquely above the wire and along the axial direction of the wire, with light reflected by the wire received on the opposite side of the wire. Raised portions on the surface of the wire are detected by utilizing the fact that the amount of light is diminished in the presence of raised portions. If the insulating material is transparent the light may pass through the insulating material layer and be reflected by the surface of the conductor. In that case, if the conductor has scratches on the surface, the light will be irregularly reflected with the result that the amount of light received is further diminished. Thus, not only raised portion on the insulating material layer but also scratches on the conductor surface are detected.
In general, raised portions which are formed on the insulating material layer by the presence of bubbles, dust or particles, are small while scratches formed on the surface of the conductor tend to be significantly larger. In view of this, a detecting technique was previously employed which utilized a geometrical differential system in which scratches and raised portions are discriminated from each other according to geometrical dimensional differences therebetween. Another earlier detecting technique utilized a time differential system in which dimensional differences were replaced by time differences.
However, scratches are not always formed on the conductor in the axial direction thereof. That is, scratches may also be formed in the circumferential direction. In such a case, the above-described conventional techniques cannot distinguish scratches on the conductor from raised portions on the insulating material layer.